To bring up one's accomplishments in conversation and contextualize them as a harrowing burden or the product of an accident or fluke.

Peter was telling me that he has four job offers, but he doesn't know how it happened because he's "dumber than an unfrozen cavemen." I wish that dude would just own up to his accomplishments, I'm tired of his humblebrag routine.

The Urban Dictionary Mug

The lowest, most despicable and loathsome form of self promotion, often delivered in a terse one or two fragmented sentences on social networking sites. A typical and popular approach is to use a disingenuous complaint about something, a self-deprecating statement or a comment on something completely innocuous, as a vehicle to deliver the real message, which invariably shows the person in a favourable light. In fact it shows what an attention seeking and insecure person they really are.

The Urban Dictionary Mug

When someone complains, quite often on social media, about something that they are lucky to have. The humblebrag also includes buzzwords, so as to truly "explain the conundrum".

"Filming on set is a complete test of patience! You know your in Hollywood when you have to cut every other second for a helicopter or an ambulance!" (a legitimate humblebrag that was found on Facebook)